Within the broad fields of social research and epidemiology, there has been much interest in the concept of vulnerability/invulnerability to various forms of physical, social, and psychological pathology. This is particularly true in the area of narcotic drug abuse, where certain individuals who grow up in "high risk" environments refrain from involvement with narcotic drugs while others, similarly exposed, become readily addicted. In this connection, it has also been the case that throughout history, major public health problems have been dealt with successfully only through prevention, rather than through treatment. However, successful prevention efforts require a clear understanding of etiological mechanisms. For this reason, the proposed study seeks to provide a firmer, empirical data base from which to infer etiological mechanisms in the area of narcotic drug abuse. Previous studies have invoked socioeconomic, psychological, political, biochemical, and genetic factors as possible interacting mechanisms. The proposed study would attempt to touch on many of those areas through the use of archival, interview, and psychological test data--the latter two types to be obtained from narcotic addicts and their matched controls. Two hundred fifty male addicts would initially be involved, and these would be matched, man-for-man, with controls consisting of non-addict peers from the same neighborhood. One innovative aspect would be the additional use of peer information to provide descriptions of both addicts and controls, and by doing so, to reconstruct their social and personal developments. Subsequent data analyses would be mutivariate in scope, and extensive use of factor and path analysis is anticipated. The feasibility of such an approach has recently been demonstrated in a pilot study in which the investigators contacted and interviewed ten triads, each triad consisting of an addict, his matched control, and an informant, for a total of 30 persons interviewed.